We have mapped emission from the circumstellar envelope of
the nearby carbon star IRC+10216 in the J=4-3
(\lambda0.85 mm) pure rotational lines of HCN in both the
ground and the (0,11c,0) vibrationally excited states.
We used the On The Fly (OTF) mapping technique with the
Heinrich Hertz Telescope of the Submillimeter Telescope
Observatory (SMTO) on Mt. Graham, AZ. The angular resolution
was 22\arcsec (HPBW). The (0,11c,0) state is the
lowest-lying bending mode of HCN, at an energy, E/k, of
~1050 K above ground. The two observed HCN lines are
separated by only 45 MHz and so could be observed
simultaneously, thereby minimizing relative calibration
uncertainties. The data allow us to constrain the angular
size distributions of the two transitions. We compare our
data with results of statistical equilibrium models for the
excitation of HCN in the IRC+10216 circumstellar envelope to
constrain the physical conditions in the inner part of the
circumstellar envelope.